Vacuum compatible fluid sampler

ABSTRACT

A fluid sampler includes: a sample cell that includes: a substrate comprising: a first port; a second port in fluid communication with the first port; a viewing reservoir in fluid communication with the first port and the second port and that receives the fluid from the first port and communicates the fluid to the second port, the viewing reservoir including: a first view membrane; a second view membrane; and a pillar interposed between the first view membrane and second view membrane, the pillar separating the first view membrane from the second view membrane at a substantially constant separation distance such that a volume of the viewing reservoir is substantially constant and invariable with respect to a temperature and invariable with respect to a pressure to which the sample cell is subjected.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. Nos. 62/343,909, filed Jun. 1, 2016, the disclosure ofwhich is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with United States Government support from theNational Institute of Standards and Technology, an agency of the UnitedStates Department of Commerce. The Government has certain rights in theinvention.

BRIEF DESCRIPTION

Disclosed is a fluid sampler comprising: a sample cell that comprises: asubstrate comprising: a first end; a second end opposing the first end;a first surface traversing a length of the substrate from the first endto the second end; and a second surface opposing the first surface andtraversing the length of the substrate from the first end to the secondend; a first port disposed in the substrate and that receives a fluid; asecond port disposed in the substrate and in fluid communication withthe first port; a viewing reservoir disposed on the substrate in fluidcommunication with the first port and the second port and that receivesthe fluid from the first port and communicates the fluid to the secondport, the viewing reservoir comprising: a first view membrane disposedon the first surface of the substrate; and a second view membranedisposed on the second surface of the substrate, wherein the fluid isinterposed between the first view membrane and the second view membrane;and a pillar interposed between the first view membrane and the secondview membrane, the pillar separating the first view membrane from thesecond view membrane at a substantially constant separation distancesuch that a volume of the viewing reservoir is substantially constantand invariable with respect to a temperature and invariable with respectto a pressure to which the sample cell is subjected, wherein the pillar,the first view membrane, and the second view membrane are monolithic.

Disclosed also is a process for selectively removing a sacrificialmember from a composite structure, the process comprising: providing afirst structural layer; disposing the sacrificial member on the firststructural layer, the sacrificial member comprising chromium oxide;disposing a second structural layer on the sacrificial member such that:the sacrificial member is interposed between the first structural layerand the second structural layer, and a composite structure is formed bythe first structural layer and the second structural layer; contactingthe sacrificial member with an etchant, the etchant being selective toetch chromium oxide and substantially inert with respect to etching thecomposite structure; and selectively etching the sacrificial member bythe etchant to selectively remove the sacrificial member from thecomposite structure, wherein the first structural layer and the secondstructural layer are spaced apart by a separation distance by removal ofthe sacrificial member.

Further discloses is a process for making a sample cell, the processcomprising: providing a substrate; disposing a first structural layer ona second surface of the substrate; disposing a third structural layer onthe first surface of the substrate; disposing a first oxide layer on thefirst structural layer: disposing a plurality of electrodes on the firstoxide layer; disposing a sacrificial member on the first oxide layer,the sacrificial member comprising: chromium oxide; a first thickness incontact with a portion of each electrode; and a second thickness that isless than then the first thickness in an area on the substrate thatcorresponds to a viewing reservoir; forming a plurality of apertures inthe sacrificial member; disposing a second oxide layer on thesacrificial member such that the sacrificial member is interposedbetween the second oxide layer and the first structural layer; disposinga second structural layer on the second oxide layer such that thesacrificial member is interposed between the second structural layer andthe first structural layer; etching the third structural layer to exposethe substrate at the first surface; forming an etchant trench on thesecond surface; etching a portion of the substrate from the firstsurface to the second surface to expose a portion of the firststructural layer in an area that corresponds to a viewing reservoir anda fluid port; and selectively etching the sacrificial member removingthe sacrificial member from between the first structural layer and thesecond structural layer to form the sample cell.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike.

FIG. 1 shows a perspective view of a fluid sampler that includes asample cell;

FIG. 2 shows a top view of the fluid sampler shown in FIG. 1;

FIG. 3 shows a bottom view of the fluid sampler shown in FIG. 1;

FIG. 4 shows a cross-section along line A-A of the fluid sampler shownin FIG. 2 according to an embodiment;

FIG. 5 shows a cross-section along line B-B of the fluid sampler shownin FIG. 2;

FIG. 6 shows a cross-section along line A-A view of the fluid samplershown in FIG. 2 according to an embodiment;

FIG. 7 shows a cross-section along line B-B of the fluid sampler shownin FIG. 2;

FIG. 8 shows a perspective view of a fluid sampler that includes asample cell;

FIG. 9 shows a top view of the fluid sampler shown in FIG. 8;

FIG. 10 shows a bottom view of the fluid sampler shown in FIG. 8;

FIG. 11 shows a cross-section along line A-A of the fluid sampler shownin FIG. 9 according to an embodiment;

FIG. 12 shows a cross-section along line B-B of the fluid sampler shownin FIG. 9;

FIG. 13 shows a perspective view of a fluid sampler that includes asample cell having a fluid reservoir;

FIG. 14 shows a top view of the fluid sampler shown in FIG. 13;

FIG. 15 shows a bottom view of the fluid sampler shown in FIG. 13;

FIG. 16 shows a cross-section along line A-A of the fluid sampler shownin FIG. 14 according to an embodiment;

FIG. 17 shows a cross-section along line B-B of the fluid sampler shownin FIG. 14;

FIG. 18 shows a top perspective view of a fluid sampler that includes asample cell having a fluid reservoir;

FIG. 19 shows a bottom perspective view of the fluid sampler shown inFIG. 18;

FIG. 20 shows a top view and bottom view of the fluid sampler shown inFIG. 18;

FIG. 21 shows a side views of the fluid sampler shown in FIG. 18according to an embodiment;

FIG. 22 shows an exploded view of the fluid sampler shown in FIG. 18;

FIG. 23 shows a perspective view of a fluid sampler that includes asample cell and fluid line;

FIG. 24 shows a perspective view of a fluid sampler that includes asample cell and fluid line;

FIG. 25 shows a perspective view of a holder;

FIG. 26 shows an exploded view of the holder and components shown inFIG. 25;

FIG. 27 shows a top view of the holder shown in FIG. 25;

FIG. 28 shows a side view of the holder shown in FIG. 25;

FIG. 29 shows a cross-section along line A-A of the holder shown in FIG.27;

FIG. 30 shows a perspective view of a transfer arm;

FIG. 31 shows an exploded view of the transfer arm shown in FIG. 30;

FIG. 32 shows a top view of the transfer arm shown in FIG. 30;

FIG. 33 shows a cross-section along line A-A of the transfer arm shownin FIG. 32;

FIG. 34 shows structures formed in making a sample cell;

FIG. 35 shows structures formed in making a sample cell;

FIG. 36 shows structures formed in making a sample cell;

FIG. 37 shows structures formed in making a sample cell;

FIG. 38 shows structures formed in making a sample cell;

FIG. 39 shows structures formed in making a sample cell;

FIG. 40 shows structures formed in making a sample cell;

FIG. 41 shows structures formed in making a sample cell;

FIG. 42 shows structures formed in making a sample cell;

FIG. 43 shows structures formed in making a sample cell;

FIG. 44 shows structures formed in making a sample cell;

FIG. 45 shows structures formed in making a sample cell;

FIG. 46 shows structures formed in making a sample cell;

FIG. 47 shows structures formed in making a sample cell;

FIG. 48 shows structures formed in making a sample cell;

FIG. 49 shows structures formed in making a sample cell;

FIG. 50 shows structures formed in making a sample cell;

FIG. 51 shows structures formed in making a sample cell;

FIG. 52 shows structures formed in making a sample cell;

FIG. 53 shows structures formed in making a sample cell;

FIG. 54 shows structures formed in making a sample cell;

FIG. 55 shows structures formed in making a sample cell;

FIG. 56 shows a graph of signal-to-noise ratio versus liquid thickness;

FIG. 57 shows a graph of deflection versus spacing in panel A and agraph of deflection versus pressure in panel B;

FIG. 58 shows structures formed in making a sample cell;

FIG. 59 shows a micrograph of a viewing reservoir in panel A and a graphof thickness there is a distance and panel B;

FIG. 60 shows a transmission electron microscope image of a nanorod inpanel A and a Fourier Transform of the image in panel B;

FIG. 61 shows a transmission electron microscopic image of ananoparticle cluster in panel A and a high-resolution scanningtransmission electron microscope image of the nanoparticle cluster;

FIG. 62 shows a graph of counts versus energy loss in panel A and agraph of counts versus energy loss in panel B; and

FIG. 63 shows a graph of counts versus energy loss.

DETAILED DESCRIPTION

A detailed description of one or more embodiments is presented herein byway of exemplification and not limitation.

It has been discovered that a fluid sampler herein includes a monolithicsample cell for imaging and spectroscopy, of a fluid, e.g., a thinliquid layer. The fluid sampler provides for encapsulating and obtaininghigh-resolution imaging and spectroscopic measurements of the fluid,e.g., in a transmission electron microscope (TEM). The sample cell canbe nanofabricated so that the fluid is separated from vacuum of the TEM.Moreover, the fluid sampler provides fluid flow, combining, heating, andapplication of voltage for, e.g. electrochemical studies. Additionally,the fluid sampler is vacuum compatible and includes a plurality ofinputs (e.g., an electrical feedthrough) for communication with anexterior of the TEM's.

In an embodiment, with reference to FIG. 1, FIG. 2, FIG. 3, FIG. 4, andFIG. 5, fluid sampler 100 includes sample cell 200 that includes:substrate 2 including: first end 4; second end 6 opposing first end 4;first surface 8 traversing a length of substrate 2 from first end 4 tosecond end 6; and second surface 32 opposing first surface 8 andtraversing the length of substrate 2 from first end 4 to second end 6;first port 16 bounded by wall 18 disposed in substrate 2 and thatreceives a fluid; second port 24 bounded by wall 26 disposed insubstrate 2 and in fluid communication with first port 16; viewingreservoir 10 bounded by wall 12 disposed on substrate 2 in fluidcommunication with first port 16 and second port 24 and that receivesthe fluid from first port 16 and communicates the fluid to second port24, viewing reservoir 10 including: first view membrane 34 disposed onfirst surface 8 of substrate 2; and second view membrane 36 disposed onsecond surface 32 of substrate 2, wherein the fluid when present isinterposed between first view membrane 34 and second view membrane 36;and pillar 14 interposed between first view membrane 34 and second viewmembrane 36, pillar 14 separating first view membrane 34 from secondview membrane 36 at a substantially constant separation distance D1 suchthat a volume of viewing reservoir 10 is substantially constant andinvariable with respect to a temperature and invariable with respect toa pressure to which sample cell 200 is subjected. Here, pillar 14, firstview membrane 34, and second view membrane 36 are monolithic.

Sample cell 200 also can include first conduit 20 bounded by wall 22such that first conduit 20 is in fluid communication with first port 16and viewing reservoir 10 and interposed between first port 16 andviewing reservoir 10, wherein first conduit 20 communicates the fluidfrom first port 16 to viewing reservoir 10. Sample cell 200 also caninclude second conduit 28 bounded by wall 30. Second conduit 28 is influid communication with second port 24 and viewing reservoir 10 andinterposed between second port 24 and viewing reservoir 10, whereinsecond conduit 28 communicates fluid from viewing reservoir 10 to secondport 24.

In an embodiment, as shown in FIG. 6 (an exemplary cross-section throughline A-A of FIG. 2), cell 200 includes recess 42 bounded by wall 44 atviewing reservoir 10 to provide a selected thickness for viewingreservoir 10. Here, first end 4 can have thickness D2 that is differentthan thickness D1 of viewing reservoir 10. Moreover, first view membrane34 and second view membrane 36 of viewing reservoir 10 respectively havethicknesses (D3, D4) that can be the same or different from each other.

In an embodiment, with reference to FIG. 7 (an exemplary cross-sectionthrough line B-B of FIG. 2), a physical geometry (e.g., a contour of abounding wall 40) of first conduit 20 provides microfluidic flow offluid from first port 16 and transitions microfluidic flow tonanofluidic flow into viewing reservoir 10. Similarly, a physicalgeometry of second conduit 28 can provide nanofluidic flow of fluid fromviewing reservoir 10 and can transition the nanofluidic flow tomicrofluidic flow to second port 24. As a result, conduit (20, 24)provide microfluidic flow of the fluid, and viewing reservoir 10provides nanofluidic flow of the fluid.

According to an embodiment, with reference to FIG. 8, FIG. 9, FIG. 10,FIG. 11, and FIG. 12, sample cell 200 includes first electrode 52disposed on substrate 2 and in electrical communication with first port16; and second electrode 50 disposed on substrate 2 and in electricalcommunication with second port 24. First electrode 52 and secondelectrode 50 produce an electric field through the fluid disposed inviewing reservoir 10 in response to application of a first electricpotential to first electrode 52 and application of a second electricpotential to second electrode 50. In this manner, the fluidelectrokinetically flows from first port 16 and through viewingreservoir 10 to second port 24 in response to a presence of the electricfield.

In an embodiment, with reference to FIG. 13, FIG. 14, FIG. 15, FIG. 16,and FIG. 17, fluid sampler 100 includes fluid container 3 disposed onsubstrate 2 of sample cell 200. Fluid container 3 can include firstfluid reservoir 5 bounded by wall 7 in fluid communication with firstport 16 and that stores fluid for communication to first port 16 andcommunicates fluid with first port 16. Fluid container 3 also caninclude second fluid reservoir 9 bounded by wall 11 and in fluidcommunication with second port 24. Here, second fluid reservoir 9 storesfluid for communication with second port 24; and communicates fluid withsecond port 24. In an embodiment, lid 21 is disposed on fluid reservoir(5, 7, and the like) to contain the fluid on sample cell 200. In anembodiment, lid 21 seals the fluid in fluid container 3 and ports (16,24) conduits (20, 28) and viewing reservoir 10. Fluid can be introducedin to fluid reservoirs (e.g., 5, 7) such that sample cell 200 can bedisposed in a vacuum chamber in an absence of further introduction offluid into fluid container 3 from an external source. In an embodiment,fluid container 3 can be interfaced to an external fluid source whilebeing disposed, e.g., in a vacuum chamber for fluid communication of thefluid between fluid container 3 and the external fluid source (e.g., seeFIG. 23). A number of fluid reservoirs can be selected based on a numberof fluid ports (e.g., 16, 24, and the like) disposed on substrate 2. Thefluid disposed in the different fluid reservoirs (e.g., 5, 9, and thelike) can be the same or can be different.

Electrodes (e.g., 50, 52, and the like) provide electrical connectionsfor heating, temperature sensing, moving components, electrical biasing,and the like of sample cell 200.

In an embodiment, with reference to FIG. 18, FIG. 19, FIG. 20, FIG. 21,FIG. 22, sample cell 200 can include a plurality of fluid ports (16, 24,21, 23) in fluid communication with viewing reservoir 10; a plurality ofpillars 14 disposed in viewing reservoir 10 and interposed between firstview membrane 34 and second view membrane 36; plurality of conduits (20,28) that communicates fluid from the plurality of fluid ports (16, 24,21, 23) and viewing reservoir 10; a plurality of electrodes (50, 52) inelectrical communication with and exposed to fluid ports (16, 24, 21,23); and flow container 3 disposed on substrate 2 and including aplurality of fluid reservoirs (5, 9, 13, 17) that are in fluidcommunication with fluid ports (16, 24, 23, 21), wherein led 21 isdisposed on fluid reservoirs (5, 9, 13, 17) to seal the fluid in samplecell 200. Although flow container 3 is shown as disposed on firstsurface 8, and electrodes (50, 52) are disposed on second surface 32, itis contemplated that any permutation of the locations and arrangementsof fluid container 3 and electrodes (50, 52) can be provided onsubstrate 2.

In an embodiment, with reference to FIG. 23, fluid sampler 100 caninclude fluid line 300 connected to fluid container 3. Fluid line 300communicates fluid with fluid reservoir (e.g., 5, 9, and the like). Anumber of fluid lines 300 can be selected based on a number of fluidreservoirs disposed in fluid container 3. In an embodiment, fluidsampler 100 includes: first gas line 300A in fluid communication withfirst fluid reservoir 5 and that supplies the fluid to first reservoir5; and second gas line 300B in fluid communication with second fluidreservoir 9 and that receives the fluid from second reservoir 9, suchthat the fluid flows from first fluid line 300A to first fluid reservoir5, from first fluid reservoir 5 to viewing reservoir 10, from viewingreservoir 10 to second port 24, and from second port 24 to second fluidline 300B.

In an embodiment, with reference to FIG. 24, sample cell 200 includeselectrical lines 400 in communication with electrodes (50, 52, and thelike) and heater 402 disposed at second end 6. A sample, e.g., a solidsample can be disposed on heater 402 and probed by a probe beam (e.g.,electron beam, laser beam, and the like. Heater 402 can heat sample cell200 and the sample disposed thereon.

In an embodiment, with reference to FIG. 25, FIG. 26, FIG. 27, FIG. 28,FIG. 29, fluid sampler 100 includes holder 202 in which sample cell 200is disposed. Holder 202 includes transmission aperture 208 bounded bywall 220 and arranged to be transmissively coincident with viewingreservoir 10 of sample cell 200 such that a probe beam (e.g., anelectron beam, laser beam, neutron beam, X-ray beam, and the like)subjected to fluid sampler 100 is transmitted tandemly throughtransmission aperture 208 and viewing reservoir 10. Additionally, holder202 includes a plurality of electrical contactors 226 disposed inelectrode member 224. In an embodiment, sample cell 200 includes firstelectrode 52 in electrical communication with first port 16; and secondelectrode 50 in electrical communication with second port 24, and holder200 to includes electrode member 224 that includes: first electricalcontactor 226A (e.g., a pogo pin) in electrical communication with firstelectrode 52 through mechanical engagement with first electrode 52; andsecond electrical contactor 226B (e.g., a pogo pin) in electricalcommunication with second electrode 50 through mechanical engagementwith second electrode 50. Here, first electrode 52 and second electrode50 can produce an electric field in response to application of a firstelectric potential to first electrode 52 from first electrical contactor226A and application of a second electric potential to second electrode50 from second electrical contactor 226B. In this manner, the fluidelectrokinetically flows from first port 16 and through viewingreservoir 10 to second port 24 in response to presence of the electricfield.

Holder 202 can include lidded compartment 214 in which sample cell 200and electrode member 224 are disposed. Lidded compartment 214 includeslid 210; lid 206 disposed on and in mechanical contact with lid 210; andarmature receiver 212 disposed on lidded compartment 214 and thatreceives transfer arm 250 (see, e.g., FIG. 30). Lid 206 and lid 210bound internal compartment 222 in which sample cell 200 is disposed. Lid206 of lidded compartment 214 can include transmission aperture 208 totransmit the probe beam there is through to viewing reservoir 10 ofsample cell 200; fastener hole 216 to receive a fastener (e.g., ascrew); prong the 236 disposed at and projecting from a first end of lid206 to mechanically engage body 204; and hook 218 disposed at a secondend of lid 206, wherein hook 218 mechanically engages lid 210 byinserting tab 240 of lid 210 between hook 218 and hook 218 of lid 206.Additionally, lid 206 can include a spring member (e.g., a leaf spring)to mechanically engage first surface 8 of sample cell 200 and to imparta force on sample cell 200 so that electrodes (50, 52) of sample cell200 are pressed against electrical contactors 226 of electrode member224.

Lid 210 can include transmission aperture 208 to be transmissivelycoincident with transmission aperture 208 of lid 206; and tab 240 tomechanically engage with hook 218 of lid 206. Body 204 receiveselectrode member 224. Electrode member 224 includes electricalcontactors 226 disposed in electrode receivers 228 that are disposed onplatform 230. Platform 230 can be offset from platform 232 at step edge234. Step edge 234 can engage first end 4 of sample cell 200. Electricalcontactors 226 received in electrode receivers 228 of platform 230 canbe held there in by electrode stay 226. Electrode stay 226 can beconnected to (e.g., adhered, fastened, and the like) to electro member224 and can include aperture is 227 to receive a portion of electricalcontactors 226. Further, Armature receiver 212 can include receptacle214 that receives transfer arm 250. It is contemplated that receptacle214 can include a feature (e.g., threading, slot, groove, alignment pin,and the like) that engages with transfer arm 250.

It is contemplated that holder 202 receives elements (e.g., electricalwiring, fluid line 300, and the like) to interface with sample cell 200.In this manner, sample cell 200 communicates with external sources(e.g., an electrical source, fluid source, and the like). Moreover,holder 202 provides an off-set or non-symmetric placement of sample cell200 disposed in holder 202 with respect to transfer arm 250 and providea space between pole pieces in a TEM so that space is available belowsample holder 202 to allow other diagnostic tools to be installed in aTEM vacuum chamber. Lidded compartment 214 provides engagement of tab240 with hook 218 so that sample cell 200 maintains alignment while lids(210, 206) are installed. Lidded compartment 214 can include a leafspring for a force to maintain a position of sample cell 200 in internalcompartment 222 and during probing of fluid in viewing reservoir 10 ofsample cell 200. The interlocking design allows for the installation ofa locking screw to secure the lid without the risk of samplemisalignment. Since clamping and interlocking of lid (206, 210) isoffset from a centerline of transfer arm 250, a central region oftransfer arm 250 provides communication of electrical wire and fluidlines and being vacuum tight and compatible.

In an embodiment, with reference to FIG. 30, FIG. 31, FIG. 32, and FIG.33, fluid sampler 100 includes transfer arm 250 on which holder 202 isdisposed. Transfer arm 250 includes armature 252 including: firstarmature end 254 that is received by armature receiver 212 of holder202; second armature end 256 that is arranged opposite first armatureend 254 and distal to armature receiver 212; electrical feedthrough 258disposed at second armature end 256; and gasket receiver 258 thatreceives a gasket (e.g., an O-ring) for producing a vacuum seal incombination with a vacuum chamber. Transfer arm 250 also can includealignment pin 260 disposed on armature 252, handle 264 disposed atsecond armature end 256, and the like. According to an embodiment,transfer arm 250 further includes: a plurality of wires 262 inelectrical communication with electrical feedthrough 258. Wire 262 caninclude a first wire to communicate the first electric potential fromelectrical feedthrough 258 to first electrical contactor 226A of holder202; and a second wire to communicate the second electric potential fromelectrical feedthrough 258 to second electrical contactor 226B. A numberof wires 262 can be selected based on a number of electrical contactors226 or electrodes (e.g., 50, 52). Electrical wires 262 can beindependent components or can be coupled together as a group, e.g., in aprinted flexible cable, a printed circuit board, a coaxial cable, andthe like. It is contemplated that transfer arm 250 can include aradiation shield disposed therein. The radiation shield can include amaterial (e.g., a metal or alloy that includes an element with a highatomic number such as 82) that blocks certain radiation (e.g., X-rays)from propagating from sample cell 200 to second armature end 256. Theradiation shield can be a foil, block, and the like.

Transfer arm 250 can be monolithic or a plurality of parts and have alength selected for inserting sample cell 200 into a vacuum chamberwhile handle 264 extends external to the vacuum chamber. Moreover, firstArmature end 254 of transfer arm 250 can include a threaded portion tomechanically engage with receptacle 214 of holder 202.

In fluid sampler 100, sample cell 200 includes viewing reservoir 10 thatcan have a shape (e.g., circular, square, polygonal, and the like)effective for viewing fluid disposed therein from first view membrane 34to second view membrane 36. In an embodiment, viewing reservoir 10 has arectangular shape (e.g., as shown in FIG. 2) with a length L1 and widthD2, wherein sample cell 200 has width W1. Moreover, length L1 can befrom 10 micrometers (μm) to 2000 μm, specifically 20 μm to 500 μm, andmore specifically from 100 μm to 200 μm. Width W1 and width W2independently can be from 2 millimeters (mm) to 10 mm, specifically 4 mmto 8 mm, and more specifically from 4 mm to 6 mm.

A number of pillars 14 is selected to provide substantially constantseparation distance D1. Separation distance D1 can be from 10 nm to 1000nm, specifically 20 nm to 500 nm, and more specifically 50 nm to 200 nm.The number of pillars 14 can be, e.g., from 1 to 1,000,000 and selectedbased on a surface area of first view membrane 34 or second viewmembrane 36. A cross-sectional thickness of pillars can be from 10 nm to1000 nm, specifically 20 nm to 500 nm, and more specifically 25 nm to 50nm. Neighboring pillars 14 can have pitch P from 400 nm to 50000 nm,specifically 1000 nm to 4000 nm, and more specifically 1000 nm to 2000nm. Pillars 14 can have a same shape or different shapes from oneanother. The shape of pillars 14 independently can be columnar,cylindrical, frustoconical, polygonal, irregular, contoured, and thelike. Pillar 14 can be solid or have an internal cavity that provides astructure to pillar 14 such as an annular shape (e.g., wherein pillar 14is a frustocone or an annular frustocone (i.e., a frustocone with anannular cross-section)). An aspect ratio (i.e., D1:T (see, e.g., FIG. 4)of pillar 14 can be any ratio effective to provide a substantiallyconstant separation D1 between view membranes (34, 36). Exemplary aspectratios (D1:T) of pillar 14 is from 1:10⁶ to 10⁶:1, specifically 10:1 to0.01:1, and more specifically, from 1:1 to 0.1:1.

Pillars 14 provide substantially constant separation distance D1 betweenfirst view membrane 34 and second view membrane 36, wherein under acompression force (due to a compressive stress) subjected to pillar 14across first view membrane 34 and second view membrane 36, separationdistance D1 is conserved at pillar 14. Moreover, under a tensive force(due to a tensile stress) subjected to pillar 14, pillar 14 providessubstantially constant separation distance D1 between view membranes(34, 36) and remains in physical contact with view membranes (34, 36).The compression force or tensive force can be a result of a temperatureor pressure under which sample cell 200 is subjected. It is contemplatedthat the temperature or pressure subjected to sample cell 200 can beexternal to sample cell 200, internal to sample cell 200 or acombination thereof. An external temperature or external pressure can besubjected to sample cell 200, e.g., at first surface 8, second surface32, or a combination from an outside of viewing reservoir 10. Internaltemperature or internal pressure can be present in viewing reservoir 10.Moreover, the pressure or temperature can be an absolute pressure orabsolute temperature based on a reference scale or can be a differentialpressure or a differential temperature across view membrane (34 or 36).Further, the pressure or temperature can be a change in the externalpressure or external temperature; or internal pressure or internaltemperature of viewing reservoir 10. Accordingly, pillar 14 separatesfirst view membrane 34 from second view membrane 36 at substantiallyconstant separation distance D1 such that separation distance D1 isinvariable with respect to a temperature and invariable with respect toa pressure to which sample cell 200 is subjected.

Sample cell 200 can include a number of layers of a same or differentmaterial. Substrate 2 can include silicon, silicon dioxide, SiO₂, glass,fused silica, SiC, sapphire, GaAs, InP, or a combination thereof. Anoxide layer can be disposed on substrate and can include silicondioxide, aluminum oxide, cerium oxide, hafnium oxide, lanthanum oxide,or other transition metal, or lanthanide oxides, or a combinationthereof. A structural layer can be included in sample cell 200 and caninclude, e.g., silicon nitride, Si, SiO₂, SiC, BN, graphene, diamond, ora combination thereof. First view membrane and the second view membraneindependently comprise silicon nitride, Si, SiO₂, SiC, BN, graphene,diamond, or a combination thereof. Electrodes (e.g., 50, 52) aredisposed on substrate 2 and can include an electrically conductivematerial such as a transition metal (e.g., tantalum and the like),conductive oxide (indium tin oxide and the like), Au, Pt, W, glassycarbon, graphene or a combination thereof.

It is contemplated that viewing reservoir 10 interposed between firstview membrane 34 and second view membrane 36 is formed by removal (e.g.,etching) of sacrificial member 68. Sacrificial member 68 can includechromium oxide that is selectively removed by a chromium oxide etchant.The chromium oxide etchant can include cerium IV, hydrochloric acid,nitric acid, perchloric acid, or a combination thereof.

The fluid can be disposed in viewing reservoir 10 of sample cell 200 andcan include a gas, a liquid, or a combination thereof. In anenvironment, the fluid is the liquid. In a certain embodiment, particles(e.g., solid, colloidal, gel, nanoparticles, microparticles, and thelike) are disposed in the liquid that flow in viewing reservoir 10. Thefluid can be hydrophobic, hydrophilic, organic, inorganic, biological,ionically charged, zwitterionic, and the like. A pressure of the fluidcan be from 10⁻⁶ Pascals (Pa) to 10⁷ Pa, specifically from 10⁻² Pa to10⁶ Pa, and more specifically from 1 Pa to 10⁵ Pa. A temperature of thefluid can be from −269° C. to 1200° C., specifically from −196° C. to1000° C., and more specifically from −100° C. to 1000° C.

Sample cell 200 is disposed in holder 202. Holder 202 can be made from avariety of materials, and elements (e.g., lid 206, lid 210, body 204,armature receiver 212, and the like) independently can be a plastic,metal, ceramic, glass, or a combination thereof. In an embodiment,holder 202 includes Titanium. To allow the device to be used in SEM andTEM systems, the components of the Sample cell 200 and Holder 202 arenon-magnetic to not distort the electron probe beams.

Holder 202 is disposed on transfer arm 250. Transfer arm 250 can be madefrom a variety of materials, and elements (e.g., armature 252, handle264, and the like) independently can be a plastic, metal, ceramic,glass, or a combination thereof. In an embodiment, holder 202 includescopper and receives an elastomeric gasket at gasket receiver 258.

The fluid can be communicated in conduits (20, 28) hydrostatically,pneumatically, electrokinetically, under capillary flow, and the like,or a combination thereof.

In an embodiment, a process for making fluid sampler 100 includesproviding sample cell 200 disposed sample cell 200 in holder 202;disposing holder 202 on transfer arm 250.

Sample cell 200 can be made in various ways including selective removalof a sacrificial member from between view membranes (34, 36). Accordingto an embodiment, a process for selectively removing a sacrificialmember from a composite structure includes: providing a first structurallayer; disposing the sacrificial member on the first structural layer,the sacrificial member including chromium oxide; disposing a secondstructural layer on the sacrificial member such that: the sacrificialmember is interposed between the first structural layer and the secondstructural layer, and a composite structure is formed by the firststructural layer and the second structural layer; contacting thesacrificial member with an etchant, the etchant being selective to etchchromium oxide and substantially inert with respect to etching thecomposite structure; and selectively etching the sacrificial member bythe etchant to selectively remove the sacrificial member from thecomposite structure, wherein the first structural layer and the secondstructural layer are spaced apart by a separation distance by removal ofthe sacrificial member.

The process for selectively removing the sacrificial member from thecomposite structure further can include: disposing the first structurallayer on a substrate; disposing an oxide layer on the first structurallayer; disposing an electrode on the oxide layer such that thesacrificial member is partially disposed on the electrode. The processfor selectively removing the sacrificial member from the compositestructure further can include patterning the sacrificial member with aplurality of apertures prior to disposing the second structural layer.The process for selectively removing the sacrificial member from thecomposite structure further can include forming a plurality of pillarsby disposing the second structural letter in the apertures of thesacrificial member. The process for selectively removing the sacrificialmember from the composite structure further can include etching a fluidport in the substrate. The process for selectively removing thesacrificial member from the composite structure further can includeforming a viewing reservoir by selectively removing the sacrificialmember; and connecting the fluid port in the substrate to the viewingreservoir by selectively removing the sacrificial member such that thefluid port is in fluid communication with the viewing reservoir. In acertain embodiment, in the process for selectively removing thesacrificial member from the composite structure, the composite structureis sample cell 200 in which viewing reservoir 10 and fluid port (e.g.,16, 24, and the like) receive a fluid.

In an embodiment, with reference to FIG. 34, FIG. 35, FIG. 36, FIG. 37,FIG. 38, FIG. 39, FIG. 40, FIG. 41, FIG. 42, FIG. 43, FIG. 44, FIG. 45,FIG. 46, FIG. 47, FIG. 48, FIG. 49, FIG. 50, FIG. 51, FIG. 52, FIG. 53,FIG. 54, and FIG. 55, a process for making sample cell 200 includes:providing substrate 2 (FIG. 34); disposing first structural layer 62 onsecond surface 32 of substrate 2 (FIG. 35); disposing third structurallayer 64 on first surface 8 of substrate 2 (FIG. 35); disposing firstoxide layer 66 on first structural layer 62 (FIG. 36); disposing aplurality of electrodes (e.g., 50, 52) on first oxide layer 66 (FIG. 37,FIG. 38); disposing sacrificial member (68, 70, 72) on first oxide layer66 (FIG. 39, FIG. 40 (panel A: cross-section along line A-A shown inFIG. 39; panel B: cross-section along line B-B shown in FIG. 39), FIG.41, FIG. 42 (cross-section along line A-A shown in FIG. 41), sacrificialmember (68, 70, 72) including: chromium oxide, a first thickness ofsacrificial member (68, 70) in contact with a portion of each electrode(50, 52), and a second thickness of sacrificial member (72) that is lessthan then the first thickness in an area on substrate 2 that correspondsto viewing reservoir 10 (to be formed upon removal of sacrificial member72); forming a plurality of apertures 76 bounded by wall 78 insacrificial member (68, 70, 72) (FIG. 43, FIG. 44 (cross-section alongline A-A shown in FIG. 43), FIG. 45, FIG. 46 (cross-section along lineA-A shown in FIG. 45)) by: disposing photoresist mask 74 on sacrificialmember (68, 70, 72), patterning photoresist mask 74 with a plurality ofapertures 80, and removing a portion of sacrificial member (68, 70, 72)coincident with apertures 80 to form apertures 76 in sacrificial member(68, 70, 72); disposing second oxide layer 84 on sacrificial member (68,70, 72) such that sacrificial member (60, 70, 72) is interposed betweensecond oxide layer 84 and first structural layer 62 (FIG. 47,cross-sectional view); disposing second structural layer 86 on secondoxide layer 84 such that the sacrificial member (68, 70, 72) isinterposed between second structural layer 86 and first structural layer62; etching third structural layer 64 disposed on first surface 8 ofsubstrate 2 to expose a portion of substrate 2 at first surface 8 (FIG.48); forming etchant trench 90 on second surface 32 to expose a portionof oxide layer 84 (FIG. 49); etching a portion of substrate 2 from firstsurface 8 to second surface 32 to expose a portion of first structurallayer 62 in an area that corresponds to viewing reservoir 10 (to beformed) and a fluid port (to be formed) (FIG. 50); and selectivelyetching sacrificial member (68, 70, 72) to remove sacrificial member(60, 70, 72) from between first structural layer 62 and secondstructural layer 86 to form sample cell 200 (FIG. 51).

The process for making sample cell 200 further can include disposingthird oxide layer 98 on second surface 32 to fill etchant trench 90(FIG. 52: panel A top view, and panel B cross-section along line A-Ashown in panel A). The process for making sample cell 200 further caninclude disposing protective layer 310 on third oxide layer 98 (FIG.53). The process for making sample cell 200 further can include (FIG.54): patterning protective layer 310; etching third oxide layer 98 toexpose viewing reservoir 10; and etching third oxide layer 98 to exposeelectrodes (e.g., 50, 52).

In an embodiment of the process for making sample cell 200, substrate 2can include silicon; first structural layer 62 can include siliconnitride; third structural layer 64 can include silicon nitride; firstoxide layer 66 can include silicon dioxide; electrodes (e.g., 50, 52)can include tantalum; sacrificial member (68, 70, 72) can includechromium oxide; photoresist mask 74 can include a polymer; second oxidelayer 84 can include silicon dioxide; second structural layer 86 caninclude silicon nitride; third oxide layer 98 can include silicondioxide; and protective layer 310 can include a polymer such as apolyimide.

In an embodiment of the process for making sample cell 200, disposingfirst structural layer 62 on second surface 32 of substrate 2 (FIG. 35)can include physical vapor deposition, chemical vapor deposition,low-pressure chemical vapor deposition, plasma-enhanced chemical vapordeposition, atomic layer deposition, plasma-enhance atomic layerdeposition.

Disposing third structural layer 64 on first surface 8 of substrate 2(FIG. 35) can include physical vapor deposition, chemical vapordeposition, low-pressure chemical vapor deposition, plasma-enhancedchemical vapor deposition, atomic layer deposition, plasma-enhanceatomic layer deposition.

Disposing first oxide layer 66 on first structural layer 62 (FIG. 36)can include physical vapor deposition, chemical vapor deposition,low-pressure chemical vapor deposition, plasma-enhanced chemical vapordeposition, atomic layer deposition, plasma-enhance atomic layerdeposition.

Disposing electrodes (e.g., 50, 52) on first oxide layer 66 (FIG. 37,FIG. 38) can include physical vapor deposition, chemical vapordeposition, low-pressure chemical vapor deposition, plasma-enhancedchemical vapor deposition, atomic layer deposition, plasma-enhanceatomic layer deposition, and electrodeposition.

With reference to FIG. 55, disposing sacrificial member (68, 70, 72) onfirst oxide layer 66 (FIG. 39) can include physical vapor deposition,chemical vapor deposition, low-pressure chemical vapor deposition,plasma-enhanced chemical vapor deposition, atomic layer deposition,plasma-enhance atomic layer deposition.

Forming a plurality of apertures 76 bounded by wall 78 in sacrificialmember (68, 70, 72) can include (FIG. 43): disposing photoresist mask 74on sacrificial member (68, 70, 72) by spin or spray coating, patterning(by optical, electron-beam or ion-beam lithography) photoresist mask 74with a plurality of apertures 80, and removing (by application of aselective wet chemical etch, or selective reactive ion etch, ordownstream plasma) a portion of sacrificial member (68, 70, 72)coincident with apertures 80 to form apertures 76 in sacrificial member(68, 70, 72).

Disposing second oxide layer 84 on sacrificial member (68, 70, 72) suchthat sacrificial member (60, 70, 72) is interposed between second oxidelayer 84 and first structural layer 62 (FIG. 47, cross-sectional view)can include physical vapor deposition, chemical vapor deposition,low-pressure chemical vapor deposition, plasma-enhanced chemical vapordeposition, atomic layer deposition, plasma-enhance atomic layerdeposition.

Disposing second structural layer 86 on second oxide layer 84 such thatthe sacrificial member (68, 70, 72) is interposed between secondstructural layer 86 and first structural layer 62 can include physicalvapor deposition, chemical vapor deposition, low-pressure chemical vapordeposition, plasma-enhanced chemical vapor deposition, atomic layerdeposition, plasma-enhance atomic layer deposition.

Etching third structural layer 64 disposed on first surface 8 ofsubstrate 2 to expose a portion of substrate 2 at first surface 8 (FIG.48) can include the use of a selective, or timed wet chemical etch, orselective, or timed reactive ion etch, or selective, or timed downstreamplasma etch, or timed or end-pointed ion milling.

Forming etchant trench 90 on second surface 32 to expose a portion ofoxide layer 84 (FIG. 49) can include the use of a selective, or timedwet chemical etch, or selective, or timed reactive ion etch, orselective, or timed downstream plasma etch.

Etching a portion of substrate 2 from first surface 8 to second surface32 to expose a portion of first structural layer 62 in an area thatcorresponds to viewing reservoir 10 (to be formed) and a fluid port (tobe formed) (FIG. 50) can include the use of a selective, or timed wetchemical etch, or selective, or timed reactive ion etch, or selective,or timed downstream plasma etch.

Selectively etching sacrificial member (68, 70, 72) to removesacrificial member (60, 70, 72) from between first structural layer 62and second structural layer 86 to form sample cell 200 (FIG. 51) caninclude the use of a selective wet, or vapor phase chemical etch.

Disposing third oxide layer 98 on second surface 32 to fill etchanttrench 90 (FIG. 52) can include physical vapor deposition, chemicalvapor deposition, low-pressure chemical vapor deposition,plasma-enhanced chemical vapor deposition, atomic layer deposition,plasma-enhance atomic layer deposition.

Disposing protective layer 310 on third oxide layer 98 (FIG. 53) caninclude spin or spray coating.

With reference to FIG. 54, patterning protective layer 310; etchingthird oxide layer 98 to expose viewing reservoir 10; and etching thirdoxide layer 98 to expose electrodes (e.g., 50, 52) can include optical,electron-beam, or ion beam lithography, selective, or timed, wetchemical etching, or selective or timed reactive ion, or downstreamreactive plasma etching, or timed or end-pointed ion milling.

In forming sacrificial member (68, 70, 72), as shown in FIG. 55, taperedprofiles (e.g., wall 40) a broad angular distribution of atomicdeposition that occurs in atomic sputtering in combination with anundercut lift-off mask produces a smooth transition from micro- tonanoscale features to provide a flow transition from microfluidic flowto nanofluidic flow.

Fluid sampler 100 has numerous beneficial uses, including containing afluid in sample cell 200 and performing transmission electron microscopyon the fluid disposed in sample cell 200.

Fluid sampler 100 has numerous advantageous and beneficial properties.In an aspect, fluid sampler 100 provides a substantially uniform andthin fluid layer to enable high-resolution imaging and spectroscopy, ameans of confining the chemistry of interest, which may be corrosive, orotherwise deleterious to a microscope or other measurement apparatus,inside the sampler, thus protecting the microscope or other measurementapparatus and enabling the study of a wider range of chemistries, ameans of achieving higher pressures than can otherwise be attained, ameans to control fluid flows with substantially improved temporalcontrol.

The articles and processes herein are illustrated further by thefollowing Example, which is non-limiting.

EXAMPLE

High-Resolution Imaging and Spectroscopy at High Pressure in a TEM.

This Example describes quantitative core-loss electron energy-lossspectroscopy of iron oxide nanoparticles and imaging resolution of Agnanoparticles in liquid down to 0.24 nm, in both transmission andscanning-transmission modes, in a novel, monolithic liquid celldeveloped for the transmission electron microscope (TEM). At typical SiNmembrane thicknesses of 50 nm the liquid layer thickness has a maximumchange of only 30 nm for the entire TEM viewing area of 200 μm×200 μm.

Transmission electron microscope (TEM), with its ability to deliveratomic-scale spatial, and <100 meV spectroscopic resolution, has enabledcountless breakthroughs in materials science. Environmental TEMs (ETEMs)were developed to study reactions in gaseous environments. ETEMs can belimited in terms of the pressures and chemistries that can be accessed.Study of materials and processes in liquid environments is challengingand requires the use of special cells to encapsulate the liquid andprotect the microscope. Creating a thin, uniform liquid layer in adevice that permits high spatial and spectroscopic resolution wasdifficult.

Conventional liquid cells comprise a pair electron-transparent windowsbetween which a layer of liquid is sandwiched. Control over the membraneseparation is achieved by polystyrene microspheres, silicon dioxide orepoxies, or wafer bonding. Scanning TEM (STEM) imaging inmicrometer-thick layers allows atomic resolution in gases. Theseconventional two-piece cells cannot accurately and reproducibly define athin liquid layer and maintain its uniformity over a large observationarea. The pressure difference between the inside and outside of the cellcan cause significant membrane deformation (bulging) and largevariations in liquid layer thickness. Both the membrane bulging effectand the difficulty of using spacers to reliably control the liquid layerthickness pose a major challenge to atomic-resolution TEM andquantitative electron energy-loss spectroscopy (EELS).

The sample cell in this Example overcomes these limits and includes apillar-supported, monolithic liquid cell that eliminates spacers andlimits bulging. This Example shows a combination of atomic-scaleimaging, in both TEM and STEM modes, and quantitative EELS using thisdesign. We discuss the design of the sample cell and identify structuraland material parameters that affect its performance.

The effect of design parameters on the performance of the device wasconsidered. We examined membrane and liquid thickness to achieveatomic-scale resolution in TEM and STEM modes. Conventionally, the imageresolution in TEM mode for thick samples or a thick liquid cell has beenestimated by considering the effect of chromatic aberration and assumingan energy spread estimated by the so-called Landau energy distribution.This Landau distribution is observed for thicknesses larger than t/λ≈3(t is thickness and λ is the inelastic mean free path) where individualplasmon and core-loss features are obscured. Chromatic aberration causesinelastically scattered electrons to be focused to a different planefrom the elastically scattered electrons, contributing a background tothe bright-field image; therefore, there will be an increasing loss ofimage contrast as the fraction of inelastically scattered electronsrises. For a total SiN thickness of 100 nm, a 75 nm thick layer ofwater, and an accelerating voltage of 300 kV, we find that the fractionof unscattered electrons is close to 25%. The remaining 75% ofelectrons, which are scattered by the membranes and liquid, include bothinelastically and elastically scattered electrons. High-Resolutionimaging is possible with a loss in contrast and a diminishedsignal-to-noise ratio (SNR), and resolution is weakly dependent onthickness in this range.

Image resolution in thick samples in STEM mode with an annulardark-field detector is determined by either broadening of the incidentprobe by multiple scattering or SNR constraints. Conventionalexperimental measurements and calculations indicate that for thicknessesof a liquid layer below≈1 μm, resolution is determined by SNR andestimates of broadening do not match the experimentally obtainedresolution for liquid cells or samples on thick substrates. The STEM SNRis estimated by calculating the intensity reaching the detector fromelastic scattering in the liquid and membrane, which contributes thebackground, and the signal is the intensity reaching the detector viaelastic scattering from the particle of interest. This method ofcalculation is applicable for estimating the resolution on the order of≈1 nm, but will only be a rough approximation for systems which permitlattice resolution because the elastic scattering calculations do notaccount for Bragg diffraction. Nonetheless, using this method weestimate an SNR sufficient to obtain STEM resolution below 0.2 nm forthe conditions applicable to the liquid cell described here, assuming aminimum SNR of 3.

Next, we consider the constraints that must be satisfied to enablequantitative, high-resolution EELS to be performed. First we focus onthe design criteria for obtaining EELS of the liquid (rather than asolid particle in the liquid). At liquid layer thicknesses, t, much lessthan the inelastic scattering length, λ, the liquid EELS signal will besmall compared to that from the membranes, while at large thicknesses(t/λ>3) plural scattering obscures both the valence and core-lossregions. A good EELS signal can be obtained if, while minimizingmultiple scattering, each electron experiences an average of oneinelastic scattering event, i.e., t/λ should be ≈1. To make a moredetailed estimate of the optimal liquid thickness we calculate theexpected SNR of the O K core-loss edge using simulated EEL spectraassuming the atomic density of oxygen for water. The SNR is determinedby calculating the expected O K signal over a 30 eV window usinghydrogenic cross sections while the noise is calculated from the squareroot of the intensity under the same window, including the backgroundcontribution. The background intensity is given by the sum of the energylosses due to the Si L edge at 99 eV, the N K edge at 402 eV and thecombined multiple scattering from core loss and plasmon losses. Toapproximate the background intensity including multiple scattering, thecore-loss spectrum from the SiN_(x) membrane is simulated and convolutedwith a simulated low-loss spectrum. The low-loss spectrum is simulatedas a series of Gaussian plasmon peaks where the total plasmon intensityis determined by Poisson statistics for a given t/λ. The value of t/λused is the total value for the membranes and liquid, again calculatedusing an Iakoubovskii approximation. All the calculations are performedusing computer programs for the core-loss edges are approximated byusing the Sigmal3 and Sigmak3 hydrogenic cross section programs and thelow-loss is simulated by a SpecGen program. The simulations indicate anoptimal O K SNR for a liquid thickness of ≈100 nm which corresponds to atotal t/λ value of 0.9 (FIG. 1). For low-loss EELS where energy-lossfeatures from the liquid and the membrane will overlap, the membranethickness should be minimized to prevent mechanical deformation orfracture and the limits of the fabrication approach.

To estimate the capabilities of this liquid cell for core-lossspectroscopy of a nanoparticle in liquid, we calculated the expected SNRfor Fe₂O₃ for a cell with a 250 nm thick liquid layer and estimate thata 2 nm thick nanoparticle should produce a detectable signal for 1 nA ofbeam current, a 5 s dwell time and a 20 eV window over the Fe L_(2,3)edge.

The liquid layer thickness can be adjusted during the fabrication over awide range, depending on whether spectroscopic information is neededfrom the liquid itself, or from nanoparticles in solution; thinnerliquid layers being preferred for EELS analysis of nanoparticles andthicker layers for EELS of the liquid. Reducing the liquid-layerthickness below a certain value, however, will not be worthwhile if themembrane thickness cannot be reduced because the scattering from themembrane will determine the SNR for small liquid layer thicknesses.

For EELS analysis of the low-loss region for liquids where features fromthe membrane and the liquid will overlap it will be advantageous forlow-loss scattering from the liquid to dominate, requiring that theliquid t/λ be greater than that of the membrane, if λ is determinedprimarily by the low-loss intensity. For 50 nm SiN_(x) membranes andwater, the liquid layer thickness should be at least 130 nm. Low-lossintensity from the membrane can be removed from a spectrum of the liquidby deconvolving a membrane-only reference spectrum though there willalways be some loss in SNR.

Ultimately, the precise values of the desired liquid thickness willdepend on the liquid or nanoparticles being studied and the experimentto be conducted. Using calculations of SNR for the O K edge from watergives an optimal liquid thickness of ≈100 nm and based on considerationsfor low-loss spectroscopy the liquid thickness should be at least 130nm. A good target liquid thickness for EELS is then in the range of 100nm to 200 nm. In this thickness range the Fe L signal should bedetectable for hematite nanoparticles ≈2 nm in thickness.

FIG. 56 shows an estimated SNR normalized to the maximum value for the OK edge as a function of liquid thickness for a cell with two 50 nm SiNmembranes. Optimal liquid thickness for studying the O K edge of liquidsis ≈100 nm.

The sample cell is designed to resist mechanical failure. SiN membraneshave high strength and exhibit a high level of fracture toughness. Inconventional cell designs, windows are unsupported across the viewingarea (supported only at the edges of the window) and are subject topressure-driven bulging. The relationship between membrane deflectionand pressure, for a square membrane, is given by

$\begin{matrix}{P = {\frac{3.93t\;{\delta\sigma}_{0}}{a^{2}} + \frac{1.834{Et}\;\delta^{3}}{\left( {1 - v} \right)\mspace{11mu} a^{4}}}} & (1)\end{matrix}$where σ₀ is the initial stress in the membrane, E the Young's modulus, vthe Poisson's ratio, t the thickness, a the half-width of the membrane,and δ the deflection (note that for a given value of a, the deflectionis approximately a factor of 2 larger for a long rectangular membrane).Equation 1 is valid for the situation when the thickness t is muchsmaller than the half-width, a; for smaller widths, finite-elementanalysis (FEA) is necessary. The options for controlling the deflectionare limited: the size of membrane, a, can be reduced, or the initialstress increased.

Reducing the width of the membrane below approximately 20 μm isimpractical for fabrication reasons (typical wafer thickness variationscause membrane widths to vary by as much as a factor of two at thesesizes), while the initial stress cannot be increased above 1 GPa withoutcompromising the strength of the membrane. Even for a long rectangularSiN membrane of width 20 μm, thickness 50 nm, and initial stress of 0.3GPa, the center deflection for each membrane will be approximately 140nm under 1 atmosphere, translating to an undesirable liquid layerthickness variation of more than 200% for an initial cavity thickness of100 nm.

Instead of reducing the total membrane width to the level of a fewmicrometers, a more suitable alternative to achieve the desired smallmembrane deflections is to introduce regular support structures toperiodically connect the upper and lower membranes, equivalent toreducing the width, a, in equation 1, while permitting the totalmembrane width and viewing area to remain large (hundreds ofmicrometers). FEA calculations for a pillar-supported, monolithic cellshow that membrane deflections can be reduced to acceptable levels (≤20nm for ≈10⁵ Pa (1 atm) pressure) once the pillar-to-pillar separation isreduced below 2 μm to 3 μm (FIG. 57). This decouples the size of theviewing area from membrane deflection and enables precise control overthe liquid layer thickness. FIG. 57 shows (panel A) membrane deflectionas a function of pillar spacing for different pressures, and panel Bshows membrane deflection as a function of pressure for membranes ofdifferent thicknesses and a constant pillar edge-to-edge spacing of 1μm. In all cases the initial membrane stress is 180 MPa. The inset showsa finite element simulation of the deflections of a structure with amembrane thickness of 50 nm and a support pillar pitch and edge-to-edgespacing of 2 μm and 1 μm respectively. The vertical displacements in theimage are exaggerated by 5× for clarity.

With reference to FIG. 58, the sample cell was fabricated by firstdepositing a layer of SiN, followed by a layer of silicon oxide and alayer of polysilicon. Holes are then etched through the poly-Si/SiO₂bilayer to the underlying SiN before the second SiN membrane layer isdeposited. Two etch ports are opened in the upper layer of SiN on eitherside of the viewing area, and out of the electron beam path. A hot KOHetch is then used to leach out the poly-Si/SiO₂ bilayer, leaving acavity with a precisely controlled height. Because SiN etches veryslowly as compared to Si in KOH (3.3 nm/h versus 2.2 μm/min), lateraletches over hundreds of micrometers are possible in a relatively shorttime (≈2 hours), without compromising the SiN membranes, enabling thecreation of cells with large viewing areas. The etch ports also serve asin/outlets for a microfluidic system.

Again, FIG. 58 shows fabrication of the sample cell for fluids in which(panel A) LPCVD SiN is deposited on both sides of a Si wafer; panel Bshows deposition of sacrificial bilayer of poly-Si/SiO₂, wherein poly-Sietches laterally rapidly in KOH, leaving the thin SiO₂ layer to beetched vertically, and SiO₂ layer acts as a protective layer shouldmetal patterns be used on the lower SiN layer; panel C shows bilayerpatterning via photolithography and reactive ion etching; panel D showsphotoresist removal; panel E shows second LPCVD SiN deposition; panel Fshows etch ports formed in upper SiN layer by photolithography andreactive ion etch; panel G shows removal of sacrificial layer by KOHetch; panel H shows an optical micrograph of completed device (overallwidth=2 mm); inset shows higher magnification view of pillar-supportedmembrane, wherein pillar spacing is 1 μm edge-to-edge, and panel I showsa scanning electron microscope image of cross-section of cavity betweentwo pillars.

The small spacing between the membrane supports not only helps to keepdeflections at the few-nanometer level (<10 nm) when the cell is inoperation, it also serves to prevent capillary forces from collapsingand sticking together the membranes when the cell is dried afteretching, or when fluid is introduced during sample loading. TheYoung-Laplace pressure for a cylindrical meniscus of radius r andsurface energy γ is γ/r. For water (γ=0.073 J/m² at 20° C.) the pressuredifference across the meniscus in a 100 nm tall cavity is approximately1.5×10⁶ Pa (15 atm). Using Equation (1) and ignoring corrections forlarge deflections, this constrains the maximum distance between supportsto be less than 3 μm for 100 nm thick membranes. An attractive featureof such a cell is its ability to support very high pressures—up to 5×10⁶Pa (≈50 atm) before there is any danger of the membrane breaking. Thismay permit the observation of catalytic processes that occur at highpressure. Once completed, the cells can be loaded via a pulled-glassmicropipette and filled by capillary action through the etch ports. Thecells may then be sealed with UV-curing resin, or, if fluid flow isdesired, with a microfluidic system.

To demonstrate the capabilities of the cell, we have performedhigh-resolution imaging in both TEM and STEM modes using suspensions ofAg nanoparticles in water/isopropanol mixtures, and collected images andEELS data from Fe₂O₃ nanorods in water/ethanol. The data were collectedat 300 keV using both an ETEM equipped with an aberration corrector forthe image-forming lens and a non-corrected TEM, both with imagingfilters, and with the liquid cell in static (no-flow) mode. The HRTEMimages were collected with a parallel beam (convergence semi-angle α=0mrad) on the aberration-corrected ETEM. The HR-STEM images werecollected using an annular dark-field detector with collectionsemi-angles between 30 mrad and 75 mrad, and a condenser aperture-spotsize combination capable of a nominal resolution of 0.136 nm. EELS datain STEM mode (shown in panel A of FIG. 59) were collected with acollection semi-angle β=21 mrad and convergence semi-angle α=10 mrad.Additional EELS data were also acquired in TEM mode with α=2.6 mrad andβ=9.6 mrad (shown in panel B of FIG. 59). EELS data acquired under theseconditions were also used to calculate the hematite nanorod oxidationstate.

With regard to FIG. 59, panel A shows energy-filtered TEM t/λ map of acell partially-filled with a water/isopropanol mixture showing theliquid meniscus. The calibration bar is in units of t/λ. Panel B shows athickness profile taken along the line in panel A. (IMFP: Inelastic meanfree path). The maximum reduction in liquid layer thickness caused bycapillary forces in the liquid-filled region is approximately 25 nm. Thedeflection in the vapor-filled region at 10⁵ Pa (≈1 atm) is negligible.

With regard to FIG. 60, panel A shows an HRTEM image of an Fe₂O₃nanorod. Panel B shows a Fourier transform of the image in panel Ademonstrating the presence of lattice fringes out to a spacing of 0.065nm.

Panel a of FIG. 59 is a thickness map of a liquid-filled cell near aboundary with a vapor-containing region and a line profile of the map isshown in panel B. The regular array of support pillars is seen and theliquid region is on the left-hand side of the image. The thicknessprofile indicates that the membranes are bowed inward, rather thanoutward, due to the capillary force of the liquid. The t/λ value in theliquid region decreases from ≈0.9 near the pillar to ≈0.8 between thepillars. Using a known value of the liquid thickness near the pillar andaccounting for the 100 nm of SiN in the beam path indicates a λ value of≈330 nm for the liquid mixture of water and ethanol. This value issignificantly larger than values calculated for liquid water usingvarious approximations derived from measurements on solids, and theexperimentally measured value for liquid water is ≈400 nm. Using this Avalue we can deduce a variation in the liquid layer thickness from 90 nmto 66 nm going from the pillar edge to between the pillars. Nosignificant variation in these values was measurable across the entirecell viewing area.

FIG. 59 shows the HRTEM image and corresponding fast Fourier transform(FFT) demonstrating lattice fringes out to 0.065 nm of a 40 nm diameterFe₂O₃ nanorod. The image was acquired with a total SiN thickness of 100nm, and a liquid-layer thickness of ≈80 nm (≈40 nm over the nanorod) inthe beam path. 10 frames were aligned and summed for the image toimprove the SNR giving a total acquisition time of 2.5 s. The membraneand liquid contribute a background and noise, but do not preventhigh-resolution imaging. We note that the observation of a peak in theFFT corresponding to 0.065 nm does not indicate a resolution of 0.065nm, but does demonstrate good stability of the system. For thick liquidcells, the best resolution in TEM mode is achieved for particles on thelower membrane, while the opposite is true for STEM. For a particle onthe bottom membrane, beam broadening in the upper membrane and liquiddegrades the STEM resolution; in TEM mode, the image of a particle onthe upper membrane is degraded by broadening as the electrons passthrough the liquid and lower membrane. STEM images using an annulardark-field (ADF) detector offer better signal-to-noise than TEM imagesfor thick samples and have therefore been preferred previously forimaging in thick liquid layers. To explore the range of applicability ofthe top-bottom criterion we have performed lattice imaging in both STEMand TEM modes at various locations across the cell membrane area and wefind that lattice resolution is attainable on the same object in bothTEM and STEM, repeatedly and reproducibly. FIG. 60 shows an example of acluster of Ag nanoparticles exhibiting 0.24 nm lattice fringes ((111)planes of Ag) in both TEM and STEM images. This demonstrates that the“top-bottom” effect is negligible for an appropriately designed cell.

With reference to FIG. 61, panel A shows an HRTEM image of an Agnanoparticle cluster in liquid. Panel B shows an HRSTEM images of thesame cluster imaged in panel A. Both images show lattice-fringeresolution of 0.24 nm. The insets are the Fast Fourier Transforms of theimages demonstrating the resolution.

With reference to FIG. 62, panel A shows a core-loss EELS spectrum of aniron oxide nanoparticle in liquid. The ratio between the L₂ and L₃ peaksenables the identification of the iron oxidation state as Fe³⁺. Panel Bshows core-loss EELS spectrum from the liquid showing an N peak from theSiN membrane and an O peak generated primarily by the liquid.

FIG. 63 shows O K edge EELS data from a liquid-containing region and avapor-containing region of the same liquid cell after deconvolution andintensity normalization. Some of the O K signal (the vapor spectrum)comes from the SiN_(x) membranes.

Both core-loss and low-loss EELS on particles in liquid and liquidsalone are possible with the cell. Panel A of FIG. 61 shows EELS dataobtained from a ≈40 nm diameter Fe₂O₃ nanorod in water/isopropanolacquired with a total exposure time of 20 s. Near-edge fine structure isobservable in both the O K edge at 532 eV and the Fe L_(2,3) edge at 708eV despite the background from the liquid and membranes. Quantificationof the Fe oxidation state is possible by measurement of the Fe Lwhite-line ratio. A method of white-line quantification was applied to aspectrum from a hematite nanorod obtained with a 0.1 eV/channeldispersion; after background subtraction and Richardson-Lucydeconvolution with the low-loss spectrum, a double arctan function wasused to subtract the continuum contribution under the white lines andthe integrated intensity for the L₂ and L₃ peaks was obtained with 2 eVwindows. The calculated L₃:L₂ ratio is 5.67±0.1 (uncertainty is given as±one standard deviation). The uncertainty estimates are determined byassuming the uncertainty in the intensity values for each peak is givenby the square root of the intensity (Poisson statistics). Noisecontributed from the increased background intensity will increase thequantification uncertainty relative to measurements in high-vacuumconditions. However, this confirms that quantitative analysis of thenear-edge structure from particles within a liquid cell is possible.Panel B of FIG. 62 shows core-loss EELS data from a liquid mixture ofwater and ethanol. In the core-loss spectrum the N K edge from themembrane is visible as well as a small O K edge primarily from theliquid. The membrane also contributes to the O K edge, but detailedcomparison between spectra from empty cells (membranes only) ad fromcells filled with the ethanol-water mixture indicates the O K intensityincreases by more than a factor of 2 when the cell is filled withliquid. FIG. 63 shows two spectra from a cell filled with awater/ethanol mixture, one from a liquid-containing region and one froma nearby vapor-filled region; after deconvolution with the low-lossspectrum and normalization of the intensities, it is possible todetermine the O K contribution from the liquid itself. The thin vaporlayer in parts of the cell contributes a negligible O signal so the Osignal from the vapor region is from O in the membranes.

Vapor formation during imaging can create small regions of vapor underthe beam and this process can ultimately limit the time available fordata acquisition from a sample in liquid. Although this was occasionallyobserved during imaging with this cell, the data shown here were notacquired from regions where bubble formation occurred.

While one or more embodiments have been shown and described,modifications and substitutions may be made thereto without departingfrom the spirit and scope of the invention. Accordingly, it is to beunderstood that the present invention has been described by way ofillustrations and not limitation. Embodiments herein can be usedindependently or can be combined.

Reference throughout this specification to “one embodiment,” “particularembodiment,” “certain embodiment,” “an embodiment,” or the like meansthat a particular feature, structure, or characteristic described inconnection with the embodiment is included in at least one embodiment.Thus, appearances of these phrases (e.g., “in one embodiment” or “in anembodiment”) throughout this specification are not necessarily allreferring to the same embodiment, but may. Furthermore, particularfeatures, structures, or characteristics may be combined in any suitablemanner, as would be apparent to one of ordinary skill in the art fromthis disclosure, in one or more embodiments.

All ranges disclosed herein are inclusive of the endpoints, and theendpoints are independently combinable with each other. The ranges arecontinuous and thus contain every value and subset thereof in the range.Unless otherwise stated or contextually inapplicable, all percentages,when expressing a quantity, are weight percentages. The suffix “(s)” asused herein is intended to include both the singular and the plural ofthe term that it modifies, thereby including at least one of that term(e.g., the colorant(s) includes at least one colorants). “Optional” or“optionally” means that the subsequently described event or circumstancecan or cannot occur, and that the description includes instances wherethe event occurs and instances where it does not. As used herein,“combination” is inclusive of blends, mixtures, alloys, reactionproducts, and the like.

As used herein, “a combination thereof” refers to a combinationcomprising at least one of the named constituents, components,compounds, or elements, optionally together with one or more of the sameclass of constituents, components, compounds, or elements.

All references are incorporated herein by reference.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. “Or” means “and/or.” Further, the conjunction “or” is used tolink objects of a list or alternatives and is not disjunctive; ratherthe elements can be used separately or can be combined together underappropriate circumstances. It should further be noted that the terms“first,” “second,” “primary,” “secondary,” and the like herein do notdenote any order, quantity, or importance, but rather are used todistinguish one element from another. The modifier “about” used inconnection with a quantity is inclusive of the stated value and has themeaning dictated by the context (e.g., it includes the degree of errorassociated with measurement of the particular quantity).

What is claimed is:
 1. A fluid sampler comprising: a sample cell thatcomprises: a substrate comprising: a first end; a second end opposingthe first end; a first surface traversing a length of the substrate fromthe first end to the second end; and a second surface opposing the firstsurface and traversing the length of the substrate from the first end tothe second end; a first port disposed in the substrate and that receivesa fluid; a second port disposed in the substrate and in fluidcommunication with the first port; a viewing reservoir disposed on thesubstrate in fluid communication with the first port and the second portand that receives the fluid from the first port and communicates thefluid to the second port, the viewing reservoir comprising: a first viewmembrane disposed on the first surface of the substrate; and a secondview membrane disposed opposing the first view membrane on thesubstrate, wherein the fluid is interposed between the first viewmembrane and the second view membrane; and a pillar interposed betweenthe first view membrane and the second view membrane, the pillarseparating the first view membrane from the second view membrane at asubstantially constant separation distance that is invariable withrespect to a temperature and invariable with respect to a pressure towhich the sample cell is subjected, wherein the pillar, the first viewmembrane, and the second view membrane are monolithic, without thepresence of any spacer material.
 2. The fluid sampler of claim 1,further comprising: a first electrode in electrical communication withthe first port; and a second electrode in electrical communication withthe second port, wherein the first electrode and second electrodeproduce an electric field in response to application of a first electricpotential to the first electrode and application of a second electricpotential to the second electrode, and the fluid electrokineticallyflows from the first port and through the viewing reservoir to thesecond port in response to the electric field.
 3. The fluid sampler ofclaim 1, further comprising: a first conduit in fluid communication withthe first port and the viewing reservoir and interposed between thefirst port and the viewing reservoir, the first conduit communicatingthe fluid from the first port to the viewing reservoir; and a secondconduit in fluid communication with the second port and the viewingreservoir and interposed between the second port and the viewingreservoir, the second conduit communicating the fluid from the viewingreservoir to the second port.
 4. The fluid sampler of claim 3, wherein aphysical geometry of the first conduit: provides microfluidic flow ofthe fluid from the first port; and transitions the microfluidic flow tonanofluidic flow into the viewing reservoir.
 5. The fluid sampler ofclaim 3, wherein a physical geometry of the second conduit: providesnanofluidic flow of the fluid from the viewing reservoir; andtransitions the nanofluidic flow to microfluidic flow into the secondport.
 6. The fluid sampler of claim 1, further comprising: a fluidcontainer disposed on the substrate and comprising: a first fluidreservoir in fluid communication with the first port and that: storesthe fluid for communication to the first port; and communicates thefluid with the first port.
 7. The fluid sampler of claim 6, wherein thefluid container further comprises: a second fluid reservoir in fluidcommunication with the second port and that: stores the fluid forcommunication with the second port; and communicates the fluid with thesecond port.
 8. The fluid sampler of claim 1, wherein the separationdistance between the first view membrane and the second view membrane isfrom 10 nanometers (nm) to 1000 nm.
 9. The fluid sampler of claim 1,wherein the sample cell transmits electrons across viewing reservoirthrough the first view membrane, the fluid in the viewing reservoir, andthe second view membrane response to being subjected by electrons froman external electron source.
 10. The fluid sampler of claim 1, whereinthe first view membrane and the second view membrane independentlycomprise silicon nitride, silicon, silicon dioxide, silicon carbide,boron nitride, graphene, diamond, or a combination comprising at leastone of the foregoing materials.
 11. The fluid sampler of claim 1,wherein the fluid comprises a gas, a liquid, or a combination comprisingat least one of foregoing fluids.
 12. The fluid sampler of claim 1,further comprising a holder in which the sample cell is disposed. 13.The fluid sampler of claim 12, wherein the holder comprises: atransmission aperture arranged transmissively coincident with theviewing reservoir such that a probe beam subjected to the fluid sampleris transmitted tandemly through the transmission aperture and theviewing reservoir.
 14. A fluid sampler comprising: a sample cell thatcomprises: a substrate comprising: a first end; a second end opposingthe first end; a first surface traversing a length of the substrate fromthe first end to the second end; and a second surface opposing the firstsurface and traversing the length of the substrate from the first end tothe second end; a first port disposed in the substrate and that receivesa fluid; a second port disposed in the substrate and in fluidcommunication with the first port; a viewing reservoir disposed on thesubstrate in fluid communication with the first port and the second portand that receives the fluid from the first port and communicates thefluid to the second port, the viewing reservoir comprising: a first viewmembrane disposed on the first surface of the substrate; and a secondview membrane disposed opposing the first view membrane on thesubstrate, wherein the fluid is interposed between the first viewmembrane and the second view membrane; and a pillar interposed betweenthe first view membrane and the second view membrane, the pillarseparating the first view membrane from the second view membrane at asubstantially constant separation distance that is invariable withrespect to a temperature and invariable with respect to a pressure towhich the sample cell is subjected, a first electrode in electricalcommunication with the first port; and a second electrode in electricalcommunication with the second port, wherein the pillar, the first viewmembrane, and the second view membrane are monolithic; a holder in whichthe sample cell is disposed and comprising: a transmission aperturearranged transmissively coincident with the viewing reservoir such thata probe beam subjected to the fluid sampler is transmitted tandemlythrough the transmission aperture and the viewing reservoir an electrodemember comprising: a first electrical contactor in electricalcommunication with the first electrode through mechanical engagementwith the first electrode; and a second electrical contactor inelectrical communication with the second electrode through mechanicalengagement with the second electrode, wherein the first electrode andsecond electrode produce an electric field in response to application ofa first electric potential to the first electrode from the firstelectrical contactor and application of a second electric potential tothe second electrode from the second electrical contactor, and the fluidelectrokinetically flows from the first port and through the viewingreservoir to the second port in response to presence of the electricfield.
 15. The fluid sampler of claim 14, wherein the holder comprises:a lidded compartment in which the sample cell and the electrode memberare disposed.
 16. The fluid sampler of claim 15, wherein the holdercomprises: an armature receiver disposed on the lidded compartment andthat receives a transfer arm.
 17. The fluid sampler of claim 16, furthercomprising the transfer arm.
 18. The fluid sampler of claim 17, whereinthe transfer arm comprises: an armature comprising: a first armature endthat is received by the armature receiver of the holder, a secondarmature end that is arranged opposite of the first armature end anddistal to the armature receiver; an electrical feedthrough disposed atthe second armature end; and a gasket receiver that receives a gasketfor producing a vacuum seal in combination with a vacuum chamber. 19.The fluid sampler of claim 17, wherein the transfer arm furthercomprises: a plurality of wires in electrical communication with theelectrical feedthrough and comprising: a first wire to communicate thefirst electric potential from the electrical feedthrough to the firstelectrical contactor; and a second wire to communicate the secondelectric potential from the electrical feedthrough to the secondelectrical contactor.
 20. A fluid sampler comprising: a sample cell thatcomprises: a substrate comprising: a first end; a second end opposingthe first end; a first surface traversing a length of the substrate fromthe first end to the second end; and a second surface opposing the firstsurface and traversing the length of the substrate from the first end tothe second end; a first port disposed in the substrate and that receivesa fluid; a second port disposed in the substrate and in fluidcommunication with the first port; a viewing reservoir disposed on thesubstrate in fluid communication with the first port and the second portand that receives the fluid from the first port and communicates thefluid to the second port, the viewing reservoir comprising: a first viewmembrane disposed on the first surface of the substrate; and a secondview membrane disposed opposing the first view membrane on thesubstrate, wherein the fluid is interposed between the first viewmembrane and the second view membrane; and a pillar interposed betweenthe first view membrane and the second view membrane, the pillarseparating the first view membrane from the second view membrane at asubstantially constant separation distance that is invariable withrespect to a temperature and invariable with respect to a pressure towhich the sample cell is subjected, wherein the pillar, the first viewmembrane, and the second view membrane are monolithic; a fluid containerdisposed on the substrate and comprising: a first fluid reservoir influid communication with the first port and that: stores the fluid forcommunication to the first port; and communicates the fluid with thefirst port; and a second fluid reservoir in fluid communication with thesecond port and that: stores the fluid for communication with the secondport; and communicates the fluid with the second port; wherein the fluidcomprises a gas, and the fluid sampler further comprises: a first gasline in fluid communication with the first fluid reservoir and thatsupplies the gas to the first reservoir; and a second gas line in fluidcommunication with the second fluid reservoir and that receives the gasfrom the second reservoir, such that the gas flows from the first gasline to the first fluid reservoir, from the first fluid reservoir to theviewing reservoir, from the viewing reservoir to the second port, andfrom the second port to the second gas line.